In general, in order to accurately reproduce a given target color using a color printer or the like, the operator repeats color adjustment by trial and error. That is, the operator makes color adjustment of an image on a display such as a CRT, LCD, or the like to obtain a desired print result. Then, the operator actually prints that image using the color printer, and then repeats color adjustment on the display after he or she observes the print result. For example, according to Japanese Patent Laid-Open No. 2000-333032, the following method is disclosed. That is, color samples and output images are displayed on the screen, and the control prompts the operator to designate a desired color and to correct the designated color. Then, color adjustment is made to reflect the corrected color onto the output image, so that the corrected color appears on the output image smoothly (continuously) with respect to surrounding colors. As another method, a color sample as a target color is measured using a calorimeter, and an output color closest to that calorimetric value, i.e., an output color which minimizes the color difference from the target color, is output.
Furthermore, as a method of storing the spectral reflectances of respective pixels so as to spectrally reproduce colors in an image, a method of compressing and storing spectral reflectances using principal component analysis has been proposed, as described in Japanese Patent Laid-Open. No. 2001-134755.
However, colors displayed on a display are generally specified by additive color mixing of three, R, G, and B phosphors, but colors output by a print process are specified by subtractive color mixing of four color inks, i.e., cyan, magenta, yellow, and black, or six color inks including light cyan and light magenta in addition to these four colors. For this reason, the color adjustment result and actual print result may often have equal tristimulus values such as XYZ or the like but different spectral reflectances. For example, since the method described in Japanese Patent Laid-Open No. 2000-333032 attains conditional color matching, color reproduction precision lowers when a print is observed in an environment different from that in which color adjustment was made, e.g., under different illumination light sources.
In the method of minimizing the color difference between a color sample and output color, tristimulus values can be matched, but spectral reflectances cannot be matched. As a result, since the color sample and output color have different spectral reflectances, they have largely different color appearances under different illumination light sources.
The method of compressing an image using principal component analysis, as described in Japanese Patent Laid-Open No. 2001-134755, has poor compatibility with RGB data as a general image storage method, because principal component coefficients of the principal component analysis results are stored as image information.